Design of synthesis route for inorganic shape-stabilized phase change materials. Direct sol–gel process versus vacuum impregnation method

Recently, sol–gel techniques for synthesize inorganic shape-stabilized phase change materials (SS-PCMs) were proposed to successfully improve thermal properties and to accomplish real applications for latent thermal energy storage (TES). In this work, the use of sol–gel process was deeply investigated to develop inorganic SS-PCM, using tetraethyl orthosilicate (TEOS) as monomer and Na2SO4.10H2O as phase change material (PCM). In addition, the influence of pH (acid and basic hydrolysis) and PCM content in the physic and thermal properties of achieved materials were analyzed. Stabilized materials were characterized by infrared spectroscopy, X-ray diffraction, scanning electronic microscopy, scanning differential calorimetry, and thermogravimetry. The characterization results established that direct sol–gel method via acid hydrolysis showed potential to develop inorganic SS-PCMs. However, results indicate that the Na2SO4.10H2O loses water molecules during synthesis, resulting in the anhydrous compound Na2SO4-SiO2; therefore, materials were proposed for high temperature TES applications. Melting point of 880–886 °C and enthalpy of fusion of 23–100 kJ kg−1 were obtained for materials with 20–60 wt.% of PCM content. The new obtained SS-PCMs have enhanced thermal properties, compared with anhydrous Na2SO4: latent storage range RL among 0.1–3.0 °C and thermal cycle stability, for high TES. In addition, direct sol–gel technique was compared with vacuum impregnation method, employing SiO2 as support material. Impregnation procedures were not successfully achieved in this work to stabilize the PCM, which prove the superior significance of direct sol–gel method.